You and me both Peter.  The learning never stops around here. Something else to seek out and try.  Thanks Dennis, again.  ;-)  

Most mushroom compost is made from composted horse manure/straw bedding, along with a few other things. It ends up very dense humus, not something I would use alone and expect to work. It can also be laced with broadleaf herbicide residues and can vary from bag to bag/ batch to batch/ supplier to supplier/ region to region. The mushroom capitol of the world is a stone's throw away and the smell can be very potent, I am used to it but it is something you need to get used to...

Shiitakes, oysters and a few others are grown on artificial logs, made form sawdust, birdseed, and bran. That stuff seems like it would make better compost but must take at least a year or more to finish so I doubt it is used often, I know a hay farmer who spreads it on his fields after a short aging, they give it to him for free as long as he hauls it away.

Chicken manure is the nastiest stuff I have ever worked with, cant be as bad eh?

Blackfoot, I do not insert the drip line into the fill tube, I insert it next to the main trunk. I believe Bill does the same.

Coop-your Pot/Tree looks beautiful!

Anyone worry about pvc leaching. I looked into the Home Depot barrel. Seems like high density resin is usually high density density ploy ethylene and according to one blog I found that manufacturers states it's safe to grow vegies in the homedepot containers. Don't know if I'm going overboard with all this leeching of large molecules and if roots have ability to uptake them.

Nope!

Sam my father is concerned about this type of thing with plastics also. He's constantly sending me articles about Monsanto, Dupont and all related stuff about food. My father is a highly intelligent man. But honestly, I kinda listen with half and ear when he starts going on about some of this stuff.

Don't get me wrong, someones gotta pay attention to it. But I have a lot of things to worry about already. It's just not my nature to worry about everything. That doesn't mean its not a  good question.

So I saw mentioned that these need water about every four days in summer months. How does it work for winter? Also how do you tell you need water?

Devlsgro, a lot depends upon the size of the tree, size of the pot, variety, type of soil used, and air temperature. In my experience during the dead of summer I have had to water anywhere between one to two gallons per day. In the spring and fall much less. When dormant you want to give your trees only enough water to survive, therefore, when I am wintering over my SIPs, I try to get as much water out of the chamber as possible and top water the same as my other potted figs.

I don't water mine in winter if they are outside. Inside, I water them I gallon of water once a month. Why? Because my garage is insulated.

I keep mine in my unheated, uninsulated outdoor wooden shed. I empty as much water as I can out of them by tilting the pot towards the over flow hole.I then surround the pots with insulating foamcore board and a blanket or two. I rarely add any water during the winter. It is not foolproof as I've lost one or two over the years, but success rate is quite high. 

Okay thank you for your replies! It's kinda a learning what your spot needs in winter thing I guess then. I'm hoping to get a winter greenhouse up someday, well insulated and just keep it above 40. The humidity will determine how much they need water I suppose. I like that the water you give is not wasted, unlike traditional top watering.